The majority of present hearing instruments are produced as units fitting entirely within the ear or within the ear canal. These hearing aids commonly referred to as “in-the ear” or “in-the-canal” instruments. Such instruments are typically constructed as a “shell” containing a battery and the electronic components, the shell having a faceplate that typically includes one or more doors or portals providing access to the battery and electronic components.
The hearing aid shell fits substantially within the ear canal so that in use the faceplate is the only visible part of the instrument. The shell is custom molded or shaped to the inner contours of the individual users ear canal to provide a fit that is comfortable and that retains the instrument securely in the ear. The customization of the shell to each individual user requires the precise shaping of the shell to the inner contours of the individual user's ear canal, which requires that each shell be molded or cast with complex contours. In order to reduce costs, the individual shells are typically produced by a “rapid shell manufacturing” process wherein a powder or a liquid material is irradiated with a laser beam into a solid form of a desired shape. The laser beam is directed to irradiate selected small volumes of the powder or liquid to eventually cause the transformation of the entire powder or liquid into the solid in the selected and irradiated volumes and to thereby also define and form the desired shape.
A recurring problem in this and other processes for molding, casting or otherwise forming hearing aid shells, however, is that hearing aid components are relatively small, as are the available space and dimensions within a shell, so that the components must be mounted securely within a shell within very tight dimensions and tolerances. In addition, the components of the hearing aid, such as the microphone, amplifier, sound processing circuitry, sound output transducer and battery, are mounted into the shell through an opening covered by a door. The access door may be separate from or combined with a battery access opening and battery cover, and which thereby presents additional problems with respect to the dimensions of the shell. The problem is compounded in that the component access opening, and perhaps also the battery access opening and their associated doors or portals, often serve as structural elements or components for positioning and mounting the components. For example, in some prior art systems some or all of the electronic components are mounted onto a circuit board, which in turn is mounted into the shell access opening in various ways, such as by adhesives or screws into a lip formed in a rim of the shell access opening, or by mating edges of the opening and the circuit board.
For various reasons, such as inherent inaccuracies in the “rapid shell” forming processes and machines, variations and tolerances in the molding materials, and variations in temperature and humidity during the molding processes, it is difficult to achieve the necessary dimensional accuracies with rapid shell manufacturing processes, or with other processes commonly used to manufacture hearing aid shells. For example, erroneous or poor dimensional control tolerances in a shell may prevent the secure mounting of components within the shell, or may cause the components to interfere with one another. The tolerances may thereby prevent secure support or mounting between the components or between the components and shell or may place undue strains on electrical or mechanical connecting components. In the instance of a circuit board mounted onto a lip around the shell access opening, for example, the lip may be too narrow or the overlap between the edge of the circuit board and the lip insufficient to provide a secure mount, the actual opening of the shell access opening may be too small or too large, and so on. It will also be recognized that these problems and other related problems are compounded yet further when the shell access opening is of a complex shape, which will frequently occur when the components are mounted into the shell access opening as a pre-assembled unit, itself having a complex shape.